Best Specific Gravity
The best aquarium specific gravity for a saltwater aquarium is open to debate. The level of salt in an aquarium is measured in specific gravity or salinity using a Hydrometer or Refractometer. The ocean has a salinity of roughly 35ppt or specific gravity of 1.026. In general, maintaining specific gravity between 1.024 and 1.026 is considered ideal for a saltwater aquarium containing a mixture of fish, corals and other invertebrates like snails, crabs, starfish and shrimp.
Aquarium Specific Gravity Tips
On the other hand, some hobbyists keeping Fish Only aquariums maintain specific gravity between 1.019 and 1.022 because it may help reduce disease. Another economic advantage is that your aquarium uses approximately 20% less salt than a reef tank. As of right now, there is no evidence to prove that a lower salinity is directly beneficial or detrimental to the health of a fish.
Hobbyists keeping nano reef tanks may maintain their aquarium specific gravity at 1.020 to 1.023. In a small aquarium without an auto-top off system, evaporation can cause salinity to rise quickly. Starting with a lower salinity will allow the hobbyist to go a few days without topping off with little risk to their livestock. Although, the less fluctuation in specific gravity the better.
Whatever salinity you decide to keep your aquarium at, the most important thing is to keep your salinity consistent. The salinity can fluctuate from everyday evaporation and proper top off solutions should be implemented to keep the salinity stable. For greater accuracy, use a refractometer rather than a hydrometer to measure salinity.